In addition to the several fractions recovered in the initial distillation of petroleum oils or tar sand bitumen, it is common practice in the art to upgrade the heavy residium to lighter distillate material that can be used as conventional refinery feedstocks or for other useful purposes. Various methods are disclosed in the prior art for effecting such upgrading. Thus, an early patent (U.S. Pat. No. 1,876,270) discloses the conversion of higher boiling hydrocarbon oils to lower boiling compounds by reacting the charge with hydrogen in the presence of certain catalysts formed from metal compounds dissolved in the oils. The essential novelty set out in the patent was in the use of diketone compounds of the disclosed metals, particularly that of molybdenum.
Later patents disclose various metal salts of molybdenum as a means for introducing the precursor of active molybdenum sulfide catalyst into the reaction system for hydrocracking of petroleum stocks. U.S. Pat. No. 3,131,142 discloses the use of metal salts of extracted petroleum acids for this purpose, to provide concentrations of 0.1 to 1.0 weight percent of the catalytic metal based on hydrocarbon feed.
U.S. Pat. No. 3,165,463 also proposed hydroconversion operations using certain organometallic compounds dissolved in the hydrocarbon charge stock. According to the patent, these compounds are first decomposed in the presence of H.sub.2 S at temperatures up to 590.degree. F. (310.degree. C.) before reacting the mixture in the presence of hydrogen. A later patent by one of the named inventors of the '463 patent (U.S. Pat. No. 3,331,769) advocates a process in which the catalyst system of the '463 patent is passed into a reactor containing either a fixed or ebullated bed of supported catalyst. The concentration of oil soluble metal that provides the active in situ catalyst in each of the foregoing cited patents is within the 0.1 to 1.0% (by weight) range as proposed in U.S. Pat. No. 3,131,142.
U.S. Pat. No. 3,975,259 (assigned to applicants' assignee) is directed to a process in which a vacuum residuum containing relatively large quantities of combined sulfur as well as various metallic contaminants, is desulfurized. According to that patent, a hydrocarbon conversion catalyst having a nominal particle size of less than 10 microns is suspended in the feedstock and this suspension is fed, together with hydrogen-rich gas, through a contact zone at elevated temperature and pressure and at a catalyst concentration of from 20 to 5000 ppm based on fresh feed. The patent discusses the advantages resulting from the use of the advocated very small particle size catalysts especially for residium conversion, and indicates that any of the types of catalysts generally recognized as suitable in hydroconversion of hydrocarbons may be employed in the process of the patent.
U.S. Pat. No. 4,111,787 is concerned chiefly with production of normally liquid hydrocarbons from coal. As described in the patent, a heavy hydrocarbonaceous oil is subjected to hydroconversion in the presence of active catalyst in a first stage at a temperature in the range of 416.degree. to 538.degree. C. Coal is added to converted liquid oil product from the first stage and the obtained slurry subjected to a second stage treatment at a temperature in the range of 416.degree.-538.degree. C., to effect hydroconversion of the coal. The active catalyst employed in the first hydroconversion stage may preferably be obtained by a pretreating step, in which the oil to be charged to the first hydroconversion stage is admixed with a soluble metal salt as catalyst precursor and the mixture is heated in the presence of hydrogen at superatmospheric pressure, at a temperature in the range of 325.degree.-415.degree. C. to convert the soluble metal salt to the active catalyst form employed in the first stage hydroconversion. In a disclosed alternative embodiment the pretreating step may be omitted and the soluble metal salt may be dissolved directly in the oil feed charged to the first hydroconversion stage wherein the active catalyst is formed in situ.
Several more recent patents disclose processes that employ very low concentrations of finely divided metals that are active for converting petroleum residium. For example, U.S. Pat. No. 4,125,455 advocates the use of C.sub.7 -C.sub.32 fatty acid salts of group VIB metals as catalysts at concentrations below 1000 ppm. The disclosed reaction is carried out by adding to the reaction mixture very low concentrations of a material such as the therein preferred molybdenum octoate. The metal salt is transformed in situ to the active catalyst.
U.S. Pat. No. 4,134,825, among a number of other related patents to the same inventors, discloses the addition of oil soluble molybdic acid or other molybdenum compounds to the reaction feed stream to form in situ the desired active molybdenum sulfide catalyst. The '825 patent employs this technique for conversion of petroleum residium. A later patent issued to these inventors, U.S. Pat. No. 4,357,229, discloses a process in which coal is added to the feed, such that the reaction mixture contains undissolved coal macerals and inorganic minerals that are formed as the coal dissolution proceeds. It is quite possible that some of the in situ metal catalyst deposits on the insoluble mineral matter (IOM). This IOM, however, is claimed to be of very small size of the order of 5 microns or smaller, which is more than an order of magnitude smaller than the size that would be retained in the reactor.
By the processes disclosed in certain of the above cited patents high yields of desired distillate oils may be obtained but the desired high yields are associated with both high accompanying production of undesirable gaseous hydrocarbons as well as high rate of consumption of expensive hydrogen.
Among the objectives attained by the present invention is the selective production from heavy hydrocarbon oils and tar sand bitumen residues, of high yields of distillate oil at relatively lower consumption of added hydrogen.